Well, this is weird. The whole passage sees so obscure to me, I thought I'd find it in the book and see if it made nay more sense in a broader context. I went to Amazon to "search inside" Sand County Almanac. It did not find any instances of the phrase "split-rail." I searched for many other phrases in the quote posted here, and could not find the passage that Tanit quoted. Mysteriouser and mysteriouser. (No, "mysteriouser" is not really a word.)
Clive, if you think "split-rail" might be a mangling of "spiritual", what do you make of "man-earth experiences"? (Maybe "man-eating pier rats"?)
(I don't mean to make fun of your idea -- I suppose it's possible that the author used "split-rail" as some metaphor for "spiritual," but it still doesn't make much sense.)